Size-dependent enhancement of electrocatalytic oxygen-reduction and hydrogen-evolution performance of MoS_2 particles

摘要

MoS_2 particles with different size distributions were prepared by simple ultrasonication of bulk MoS_2 followed by gradient centrifugation. Relative to the inert microscale MoS_2, nanoscale MoS_2 showed significantly improved catalytic activity toward the oxygen-reduction reaction (ORR) and hydrogen-evolution reaction (HER). The decrease in particle size was accompanied by an increase in catalytic activity. Particles with a size of around 2 nm exhibited the best dual ORR and HER performance with a four-electron ORR process and an HER onset potential of -0.16 V versus the standard hydrogen electrode (SHE). This is the first investigation on the size-dependent effect of the ORR activity of MoS_2, and a four-electron transfer route was found. The exposed abundant Mo edges of the MoS_2 nanoparticles were proven to be responsible for the high ORR catalytic activity, whereas the origin of the improved HER activity of the nanoparticles was attributed to the plentiful exposed S edges. This newly discovered process provides a simple protocol to produce inexpensive highly active MoS_2 catalysts that could easily be scaled up. Hence, it opens up possibilities for wide applications of MoS2 nanoparticles in the fields of energy conversion and storage.